How does Charlotte Lucas demonstrate pragmatism?

Charlotte Lucas is critical in illustrating Austen's theme of love and marriage, which is developed through the representation of various kinds: arranged marriage after failed elopement; marriage for esteem and love; marriage for beauty and pleasure; exploitative marriage; pragmatic marriage.
Austen's favored kind of marriage is, quite naturally, marriage for esteem and love as represented by both Elizabeth and Darcy, and Jane and Bingley. Yet Austen acknowledges the pragmatic marriage, as represented by Charlotte Lucas and Mr. Collins, is a valid and viable alternative.
Austen herself had some experience with the pragmatic marriage, though her experience was one of twenty-four hours, a time period that ended with her hasty flight and a message left with her brother to be delivered to her cousin and would-be suitor. On a holiday to visit her brother, Austen's cousin proposed marriage to her, and she accepted. Overnight, she regretted this engagement and fled the scene at break of day. Yet, she has the presence of mind to understand that, for a pragmatic woman, with no lost love still kindling her heart, a pragmatic marriage was an effective solution to the social difficulties facing an unmarried woman.
Charlotte Lucas embodies this pragmatic woman and approach, although Elizabeth refuses to take her seriously down to the last:
"[It] is better to know as little as possible of the defects of the person with whom you are to pass your life." "You make me laugh, Charlotte; but it is not sound. You know it is not sound, and that you would never act in this way yourself." (Ch 6)
Charlotte, believing that happiness in marriage is a gamble,—Mr. and Mrs. Bennet affirm that couples "grow sufficiently unlike afterwards to have their share of vexation"—weighs the consequences of remaining single in her father's large household, operating on a modest budget, in a remote country village, against the consequences of marrying a foolish man with good intentions and a good position in his profession. She finds that marriage to Collins is less of a loss to her than continuing her life of dependency at her father's country home.
What is interesting is Elizabeth's staunch refusal to take Charlotte seriously, even up until Charlotte's announcement of her engagement to Mr. Collins. If we examine the evidence presented in the novel, we are faced with a married Charlotte who is happy in married life, who has shielded herself from unnecessary vexation from her husband, who enjoys the company and social advantages of her new neighbors at Rosings, and who is satisfied that her pragmatic decision was the right decision.
Charlotte's pragmatic nature is developed by Austen before her decision to marry Collins. If this were not so, we might be taken by surprise and find a logical inconsistency within Charlotte's character.
Three instances of Charlotte's development as a pragmatic character stand out. The first is her conversation with Elizabeth about whether Jane has spent sufficient time with Bingley to be able to know if she loves and would marry him.
"[If] she were married to him to-morrow, I should think she had as good a chance of happiness as if she were to be studying his character for a twelvemonth. Happiness in marriage is entirely a matter of chance."
This discussion leads into Charlotte's assertion that "it is better to know as little as possible of the defects of the person with whom you are to pass your life." While Elizabeth took her to be remarking in jest, later events concerning Collins show that she was indeed quite serious.
The second instance of Austen's development of Charlotte as a pragmatic woman occurs at the Netherfield ball during which Darcy surprises Elizabeth by requesting the pleasure of dancing with her. Elizabeth accepts him out of stunned surprise rather than out of willingness. While Elizabeth "was left to fret over her own want of presence of mind," Charlotte took the opportunity to caution her with pragmatic appropriateness not to be prejudiced by Wickham's charm and neglectful of Darcy's "consequence":
When the dancing recommenced, however, and Darcy approached to claim [Elizabeth's] hand, Charlotte could not help cautioning her in a whisper, not to be a simpleton, and allow her fancy for Wickham to make her appear unpleasant in the eyes of a man ten times his consequence.
The third instance relates to the aftermath of Collins' rejection by Elizabeth. Collins' has made his clumsy proposal. Elizabeth has refused. Mrs. Bennet is the height of dismayed and distraught. She is about to assure Collins that she will do everything to persuade Elizabeth that it is her best interest to accept Collins.
Elizabeth and all the other daughters quickly leave the room, but Charlotte, who has been visiting and has heard everything from Elizabeth, is first detained by Collins' polite inquiries after her family and then detained by curiosity. Charlotte lingers by a distant window to overhear what might be passing in so unusual a scene. This deliberate eavesdropping is a very calculated and pragmatic step, one that portends a pragmatic young woman suddenly calling to mind her own interests and concerns.
We have watched Charlotte develop and know that, while she has respect for persons of consequence, she has never said anything that sets her apart as a woman interested in material gain aside from gain in happiness and independence. Austen has used Charlotte to build a convincing case for the acceptability of a pragmatic marriage for a pragmatic woman.
"I am not romantic, you know; I never was. I ask only a comfortable home; and considering Mr. Collins's character, connection, and situation in life, I am convinced that my chance of happiness with him is as fair as most people can boast on entering the marriage state."